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    <script>
      // 原地修改，每次都将计算结果赋值给自己
      let n = 10;
      n = n + 1; //n=11=10+1
      n = n + 2; //n=13=11+2
      n = n - 3; // n=13-3=10
      n = n / 2; //5
      n = n * 3; //15
      console.log(n); //
    </script>
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